1. Field of the Invention
The present invention relates to the field of motor vehicles and, more particularly, to the steering column and steering wheel of a motor vehicle and to energy absorbing structural components for the latter.
2. Description of the Prior Art
Various improvements have been made in recent years in the structure and design of motor vehicles, including improvements which, like the present invention, are aimed at the protection of the driver of the motor vehicle in the case of a violent collision. The purpose of the present invention is specifically to reduce the effects of the so-called secondary collision which takes place inside the motor vehicle between the driver and the motor vehicle, split seconds after the primary collision between the vehicle and whatever it is colliding with. This secondary collision is particularly severe in the case of a head-on collision, when the vehicle is decelerated abruptly and the driver's kinetic energy propels him forwardly against the steering wheel and dashboard.
Various means and devices aimed at the absorption, i.e., the gradual transfer, of the impact energy from the driver to the steering wheel and steering wheel column during the secondary collision have been suggested in the past. There are basically two ways of absorbing impact energy of this type: elastic absorption, as by means of a spring or some other resiliently deformable member, and plastic absorption, which takes place when the energy is converted into permanent deformation work on the energy absorbing member. While the first type of energy absorption can take place repeatedly, the second type normally renders the energy absorbing member unserviceable for future use. However, the second type of energy absorption is much superior to the first, in that no subsequent release of the absorbed energy takes place and in that its energy absorption characteristics are more desirable, because a very small mass of material can absorb a large amount of impact energy through permanent deformation.
While some limited elastic absorption of impact energy is available with virtually every type of steering wheel, due to the natural resiliency of the steering wheel rim and/or of its spokes, the plastic absorption of impact energy in the steering wheel or in the steering wheel column has only in recent years become a serious objective. Various solutions to this problem have already been suggested, and they differ in terms of their design features, assembly arrangements, and materials utilized. As in all mass produced devices, a primary criterion for the acceptability and commercial success of a proposed solution is its manufacturing cost.